1. Field of the Invention
The present invention relates to a plasma display panel and, more particularly, to a plasma display apparatus and driving method thereof, in which an afterimage occurring when the plasma display panel is turned on can be obviated and an erroneous discharge phenomenon and damage to elements can be prevented.
2. Background of the Related Art
In general, a plasma display panel comprises a front substrate and a rear substrate. A barrier rib formed between the front substrate and the rear substrate forms one unit cell. Each cell is filled with a primary discharge gas, such as neon (Ne), helium (He) or a mixed gas of Ne+He, and an inert gas containing a small amount of xenon (Xe). If the inert gas is discharged with a high frequency voltage, vacuum ultraviolet rays are generated. Phosphors formed between the barrier ribs are excited to display images. The plasma display panel can be made thin, and has thus been in the spotlight as the next-generation display devices.
FIG. 1 shows the construction of a general plasma display panel.
As shown in FIG. 1, the plasma display panel comprises a front substrate 100 and a rear substrate 110. In the front substrate 100, a plurality of sustain electrode pairs in which scan electrodes 102 and sustain electrodes 103 are formed in pairs is arranged on a front glass 101 serving as a display surface on which images are displayed. In the rear substrate 110, a plurality of address electrodes 113 crossing the plurality of sustain electrode pairs is arranged on a rear glass 111 serving as a rear surface. At this time, the front substrate 100 and the rear substrate 110 are parallel to each other with a predetermined distance therebetween.
The front substrate 100 comprises the pairs of scan electrodes 102 and sustain electrodes 103, which mutually discharge one another and maintain the emission of a cell within one discharge cell. In other words, each of the scan electrode 102 and the sustain electrode 103 has a transparent electrode (a) formed of a transparent ITO material and a bus electrode (b) formed of a metal material. The scan electrodes 102 and the sustain electrodes 103 are covered with one or more dielectric layers 104 for limiting a discharge current and providing insulation among the electrode pairs. A protection layer 105 having Magnesium Oxide (MgO) deposited thereon is formed on the dielectric layers 104 so as to facilitate discharge conditions.
In the rear substrate 110, barrier ribs 112 of stripe form (or well form), for forming a plurality of discharge spaces, i.e., discharge cells are arranged parallel to one another. Furthermore, a plurality of address electrodes 113, which generate vacuum ultraviolet rays by performing an address discharge, are disposed parallel to the barrier ribs 112. R, G and B phosphor layers 114 that radiate a visible ray for displaying images during an address discharge are coated on a top surface of the rear substrate 110. A dielectric layer 115 for protecting the address electrodes 113 is formed between the address electrodes 113 and the phosphor layers 114.
In the plasma display panel constructed above, discharge cells are formed in plural in a matrix structure. A driving module having a driving circuit for providing a predetermined pulse is attached to the discharge cells to form a driving apparatus. The coupling relation between the plasma display panel and the driving module will be described with reference to FIG. 2.
FIG. 2 is a view for illustrating a driving apparatus of the plasma display panel in the related art. As shown in FIG. 2, the driving apparatus of the plasma display panel in the related art has discharge cells, which are formed in plural in matrix form, attached to the plasma display panel, so that a predetermined pulse is supplied to the discharge cells.
The driving apparatus of the plasma display panel comprises a data aligner 200, a timing controller 201, a data driver 202, a scan driver 203 and a sustain driver 204, as shown in FIG. 2.
The data aligner 200 of the driving apparatus in the related art aligns externally input image data and applies them to respective address electrodes X1 to Xm. The aligned data are supplied to the address electrodes X1 to Xm of the plasma display panel 205 through the data driver 202.
Furthermore, the scan driver 203 applies a scan signal and a sustain signal to scan electrodes Y1 to Yn under the control of the timing controller 201. The sustain driver 204 applies a sustain signal to each of sustain electrodes Z under the control of the timing controller 201. Through this process, the plasma display panel 205 is driven. A method of implementing gray levels of an image in the plasma display panel constructed above will be described below with reference to FIG. 3.
FIG. 3 is a view for illustrating a method of implementing gray levels of an image in the plasma display panel in the related art.
As shown in FIG. 3, in order to represent image gray levels of the plasma display panel in the related art, one frame is divided into several sub-fields having a different number of emissions. Each of the sub-fields is divided into a reset period (RPD) for initializing the entire cells, an address period (APD) for selecting a cell to be discharged, and a sustain period (SPD) for implementing gray levels depending on the number of discharges.
For example, if it is sought to display images with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields (SF1 to SF8) as shown in FIG. 2. Each of the eight sub-fields (SF1 to SF8) is again divided into a reset period, an address period and a sustain period.
The reset period and the address period of each sub-field are the same every sub-field. An address discharge for selecting a cell to be discharged is generated because of a voltage difference between the address electrodes and the scan electrodes (i.e., transparent electrodes). The sustain period is increased in the ratio of 2n (where n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field.
Since the sustain period is varied every sub-field as described above, gray levels of an image are represented by controlling the sustain period of each sub-field, i.e., a sustain discharge number. A driving waveform depending on the driving method of the plasma display panel will be described below with reference to FIG. 4.
FIG. 4 shows a driving waveform depending on the driving method of the plasma display panel in the related art.
As shown in FIG. 4, the plasma display panel is driven with one frame being divided into a reset period for initializing the entire cells, an address period for selecting a cell to be discharged, a sustain period for sustaining the discharge of the selected cell and an erase period for erasing wall charges within discharged cells.
The reset period is divided into a setup period and a setdown period.
In the setup period of the reset period, a ramp-up waveform (Ramp-up) is applied to the entire scan electrodes at the same time. The ramp-up waveform generates a weak dark discharge within discharge cells of the entire screen. The setup discharge causes positive wall charges to be accumulated on the address electrodes and the sustain electrodes, and negative wall charges to be accumulated on the scan electrodes.
In the setdown period of the reset period, after the ramp-up waveform is applied, a ramp-down waveform (Ramp-down), which starts falling from a positive voltage lower than a peak voltage of the ramp-up waveform up to a predetermined voltage level lower than a ground (GND) level voltage, generates a weak erase discharge within cells, thereby sufficiently erasing wall charges excessively formed on the scan electrodes. The setdown discharge causes wall charges of the degree in which an address discharge can occur stably to uniformly remain within the cells.
In the address period, while negative scan pulses are sequentially applied to the scan electrodes, data pulses of a positive voltage (Va) is applied to the address electrodes in synchronization with the scan pulse. As a voltage difference between the scan pulse and the data pulse and a wall voltage generated in the reset period are added, an address discharge is generated within discharge cells to which the data pulse is applied. Furthermore, wall charges of the degree in which a discharge can be generated when a sustain voltage (Vs) is applied are formed within cells selected by an address discharge. The sustain electrodes are supplied with a positive voltage (Vz) such that an erroneous discharge is not generated between the sustain electrodes and the scan electrodes by reducing between the sustain electrodes and the scan electrodes during the setdown period and the address period.
In the sustain period, a sustain pulse (sus) is alternately applied to the scan electrodes and the sustain electrode. In cells selected by an address discharge, a sustain discharge, i.e., a display discharge is generated between the scan electrodes and the sustain electrodes whenever the sustain pulse is applied as the wall voltage within the cell and the sustain pulse are added.
After the sustain discharge is finished, in the erase period, a voltage of an erase ramp waveform (Ramp-ers) having a narrow pulse width and a low voltage level is applied to the sustain electrodes, thereby erasing wall charges remaining within the cells of the entire screen.
Meanwhile, if a normal driving pulse is input as soon as the plasma display panel is turned on, wall charges remain within respective cells of the plasma display panel with them being displayed. Thereafter, when the plasma display panel is turned on, if a normal driving pulse is input, a problem arises because an afterimage of the degree in which a human being can see the screen, which was being displayed when the plasma display panel was turned off, appears due to the discharge of the remaining wall charges, which is incurred by the reset pulse of the driving pulse.
Furthermore, if a normal driving pulse is input as soon as the plasma display panel is turned on, the high voltages (Vs, Va) for applying the driving pulse are instantly applied. This generates an erroneous discharge phenomenon. A problem also arises because elements can be damaged due to overload of the plasma display panel.